When properly used to improve surface friction and prevent water penetration, agencies report chip sealing allows them to maintain the most square yards of pavement per dollar spent. Photos: International Slurry Surfacing Association

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By consistently devoting budgetary dollars to pavement preservation treatments, such as micro surfacing, agencies can maintain four to five times more lane-miles than if they only focus on rehabilitation.

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The International Slurry Surfacing Association (ISSA) has applied a hypothetical cost scenario to the Pavement Condition Index chart developed by the Army Corps of Engineers. In this example, a road that receives three preservation treatments over a 25-year period at $2/square yard will remain in good condition for a total cost of $6/square yard.If the road is left untreated for 11 years and pavement preservation is used as reactive maintenance to preserve the pavement, the cost will be approximately $4/square yard. Waiting this long to apply a treatment generally leads to a deteriorated road-base structure, so the reactive maintenance treatment will only last about four years, when it will require yet another treatment or rehabilitation. In comparison, if nothing is done for 12 or more years, a mill-and-fill (mill and overlay) or full rehabilitation will be required at a cost upwards of $12 to $16/square yard.

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Formula for success

“The key to implementing preventive maintenance techniques and maintaining a pavement management program is developing and maintaining an inventory of pavement condition and quantity,” says Laipple. In Overland Park, streets are broken into sections and student interns survey the same locations on a biennial basis, counting cracks and deficiencies as identified in the Federal Highway Administration's Pavement Distress Identification Manual. “We compare scores of the current assessment to those of prior assessments and monitor the rate of deterioration,” he explains.

The Pavement Condition Index, developed by the Army Corps of Engineers, is generally accepted as the industry standard for scoring pavement condition (see chart below). It provides a rational basis, calculating deterioration rate and deterioration modeling. The data can be used in conjunction with a pavement management program to develop a plan for pavement preservation, proactive maintenance, and rehabilitation.

Most of Overland Park's pavements receive some form of preventive maintenance every seven years, but in the future, Laipple may prioritize maintenance based on pavement condition and construction type rather than elapsed time between treatments.

Overland Park generally uses the following schedule for residential streets. Major maintenance at year 28 and reconstruction at year 50 may be shifted as budget allows, however preventive maintenance occurs consistently:

Most agencies know pavement preservation techniques such as slurry and micro surfacing, chip sealing, and crack treatment can extend their budgets. Now residents are beginning to understand the benefits of pavement preservation. “A mill and overlay is similar to the idea of removing the siding from your home every 25 years and replacing it with new siding. It's cheaper and more efficient to paint the siding and preserve it over time,” says Laipple.

However, pavement preservation measures don't work as reactive maintenance. If roads that are in fair-to-good condition are ignored and budget dollars are devoted only to rehabilitation of the worst roads, then overall road conditions will get poorer and agencies will always be playing catchup, even when budgets grow as the recession declines.

Micro surfacing — A mixture of aggregate, asphalt emulsion, water, and additives applied in a smooth layer over existing pavement. When applied early in the pavement's life cycle, it can cost-effectively extend surface life by seven or more years.

Slurry seal — Applied to existing pavement by a spreader box linked to the surface slurry-mixing unit. Used over newly laid pavements, slurry seal will prevent surface distresses such as the effects of weathering. Existing distresses in older pavements — surface cracking, raveling, loss of matrix, increased water and air permeability, and slipperiness due to flushing and aggregate polishing — can be corrected with a slurry application.

Crack treatments — Specialized materials are placed into prepared cracks to prevent water and incompressible intrusion into the cracks and underlying pavement layers and to reinforce the adjacent pavement. Used for pavements that primarily have working cracks (greater than 1/8-inch annual movement).